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Diffstat (limited to 'subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/itc/alg/misc/scc/SCC.java')
-rw-r--r-- | subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/itc/alg/misc/scc/SCC.java | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/itc/alg/misc/scc/SCC.java b/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/itc/alg/misc/scc/SCC.java new file mode 100644 index 00000000..de070839 --- /dev/null +++ b/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/itc/alg/misc/scc/SCC.java | |||
@@ -0,0 +1,143 @@ | |||
1 | /******************************************************************************* | ||
2 | * Copyright (c) 2010-2012, Tamas Szabo, Istvan Rath and Daniel Varro | ||
3 | * This program and the accompanying materials are made available under the | ||
4 | * terms of the Eclipse Public License v. 2.0 which is available at | ||
5 | * http://www.eclipse.org/legal/epl-v20.html. | ||
6 | * | ||
7 | * SPDX-License-Identifier: EPL-2.0 | ||
8 | *******************************************************************************/ | ||
9 | |||
10 | package tools.refinery.viatra.runtime.rete.itc.alg.misc.scc; | ||
11 | |||
12 | import tools.refinery.viatra.runtime.matchers.util.CollectionsFactory; | ||
13 | import tools.refinery.viatra.runtime.rete.itc.igraph.IGraphDataSource; | ||
14 | |||
15 | import java.util.*; | ||
16 | |||
17 | /** | ||
18 | * Efficient algorithms to compute the Strongly Connected Components in a directed graph. | ||
19 | * | ||
20 | * @author Tamas Szabo | ||
21 | * | ||
22 | * @param <V> | ||
23 | * the type parameter of the nodes in the graph | ||
24 | */ | ||
25 | public class SCC<V> { | ||
26 | |||
27 | private SCC() {/*Utility class constructor*/} | ||
28 | |||
29 | public static long sccId = 0; | ||
30 | |||
31 | /** | ||
32 | * Computes the SCCs for the given graph and returns them as a multiset. (Iterative version of Tarjan's algorithm) | ||
33 | * | ||
34 | * @param g | ||
35 | * the directed graph data source | ||
36 | * @return the set of SCCs | ||
37 | */ | ||
38 | public static <V> SCCResult<V> computeSCC(IGraphDataSource<V> g) { | ||
39 | int index = 0; | ||
40 | Set<Set<V>> ret = new HashSet<Set<V>>(); | ||
41 | |||
42 | // stores the lowlink and index information for the given node | ||
43 | Map<V, SCCProperty> nodeMap = CollectionsFactory.createMap(); | ||
44 | |||
45 | // stores all target nodes of a given node - the list will be modified | ||
46 | Map<V, Set<V>> targetNodeMap = CollectionsFactory.createMap(); | ||
47 | |||
48 | // stores those target nodes for a given node which have not been visited | ||
49 | Map<V, Set<V>> notVisitedMap = CollectionsFactory.createMap(); | ||
50 | |||
51 | // stores the nodes during the traversal | ||
52 | Deque<V> nodeStack = new ArrayDeque<V>(); | ||
53 | |||
54 | // stores the nodes which belong to an scc (there can be many sccs in the stack at the same time) | ||
55 | Deque<V> sccStack = new ArrayDeque<V>(); | ||
56 | |||
57 | boolean sink = false, finishedTraversal = true; | ||
58 | |||
59 | // initialize all nodes with 0 index and 0 lowlink | ||
60 | Set<V> allNodes = g.getAllNodes(); | ||
61 | for (V n : allNodes) { | ||
62 | nodeMap.put(n, new SCCProperty(0, 0)); | ||
63 | } | ||
64 | |||
65 | for (V n : allNodes) { | ||
66 | // if the node has not been visited yet | ||
67 | if (nodeMap.get(n).getIndex() == 0) { | ||
68 | nodeStack.push(n); | ||
69 | |||
70 | while (!nodeStack.isEmpty()) { | ||
71 | V currentNode = nodeStack.peekLast(); | ||
72 | sink = false; | ||
73 | finishedTraversal = false; | ||
74 | SCCProperty prop = nodeMap.get(currentNode); | ||
75 | |||
76 | if (nodeMap.get(currentNode).getIndex() == 0) { | ||
77 | index++; | ||
78 | sccStack.addLast(currentNode); | ||
79 | prop.setIndex(index); | ||
80 | prop.setLowlink(index); | ||
81 | |||
82 | notVisitedMap.put(currentNode, new HashSet<V>()); | ||
83 | |||
84 | // storing the target nodes of the actual node | ||
85 | if (g.getTargetNodes(currentNode) != null) { | ||
86 | Set<V> targets = g.getTargetNodes(currentNode).distinctValues(); | ||
87 | targetNodeMap.put(currentNode, CollectionsFactory.createSet(targets)); | ||
88 | } | ||
89 | } | ||
90 | |||
91 | if (targetNodeMap.get(currentNode) != null) { | ||
92 | |||
93 | // remove node from stack, the exploration of its children has finished | ||
94 | if (targetNodeMap.get(currentNode).size() == 0) { | ||
95 | targetNodeMap.remove(currentNode); | ||
96 | |||
97 | nodeStack.removeLast(); | ||
98 | |||
99 | for (V targetNode : g.getTargetNodes(currentNode).distinctValues()) { | ||
100 | if (notVisitedMap.get(currentNode).contains(targetNode)) { | ||
101 | prop.setLowlink(Math.min(prop.getLowlink(), nodeMap.get(targetNode).getLowlink())); | ||
102 | } else if (sccStack.contains(targetNode)) { | ||
103 | prop.setLowlink(Math.min(prop.getLowlink(), nodeMap.get(targetNode).getIndex())); | ||
104 | } | ||
105 | } | ||
106 | |||
107 | finishedTraversal = true; | ||
108 | } else { | ||
109 | V targetNode = targetNodeMap.get(currentNode).iterator().next(); | ||
110 | targetNodeMap.get(currentNode).remove(targetNode); | ||
111 | // if the targetNode has not yet been visited push it to the stack | ||
112 | // and mark it in the notVisitedMap | ||
113 | if (nodeMap.get(targetNode).getIndex() == 0) { | ||
114 | notVisitedMap.get(currentNode).add(targetNode); | ||
115 | nodeStack.addLast(targetNode); | ||
116 | } | ||
117 | } | ||
118 | } | ||
119 | // if currentNode has no target nodes | ||
120 | else { | ||
121 | nodeStack.removeLast(); | ||
122 | sink = true; | ||
123 | } | ||
124 | |||
125 | // create scc if node is a sink or an scc has been found | ||
126 | if ((sink || finishedTraversal) && (prop.getLowlink() == prop.getIndex())) { | ||
127 | Set<V> sc = new HashSet<V>(); | ||
128 | V targetNode = null; | ||
129 | |||
130 | do { | ||
131 | targetNode = sccStack.removeLast(); | ||
132 | sc.add(targetNode); | ||
133 | } while (!targetNode.equals(currentNode)); | ||
134 | |||
135 | ret.add(sc); | ||
136 | } | ||
137 | } | ||
138 | } | ||
139 | } | ||
140 | |||
141 | return new SCCResult<V>(ret, g); | ||
142 | } | ||
143 | } | ||